1. Field of Invention
Embodiments of the invention generally relate to systems for and methods of signal processing, and in particular, to processing a signal which includes data originating in any one of a plurality of formats which is encoded in an image.
2. Discussion of Related Art
Today, there exist many applications where media includes a plurality of signal types such as audio signals that drive sound equipment, video signals that drive video displays and graphics signals that drive graphic displays. Generally, it is desirable to synchronize each of the audio, video and graphics signals with one another to provide an integrated media display or plurality of integrated displays. The synchronization of an audio output with a video output to insure a match between a movement of the lips of a speaker in the video image and the spoken word that is being provided by the audio output at the same moment provides one example.
The availability of increasingly advanced video editing and animation systems for desktop and laptop computers provide current examples where synchronized outputs in a variety of output formats may be desired. For example, a video editing system (e.g., Adobe Premiere, Apple Final Cut Pro) may result in a composition that includes an audio signal and a video signal that should be synchronized to a common time base. Similar systems may be employed in professional studio production facilities where a studio genlock signal is available.
Software that allows users to convert presentations to video provides another example in which signals in a plurality of formats may be combined in a composition. In one specific example, a power point presentation (i.e., a graphics file) is converted to standard video format where the composition includes the video and an audio signal that is generated by a different application.
A variety of approaches have been attempted to synchronize a plurality of signals in different formats with one another. In one approach, a timing reference, for example, a genlock signal is used to synchronize a graphics frame buffer. This approach, however, requires a specialized graphics controller where a pixel clock and a synch generator of the graphics controller are each synchronized to the reference signal to provide synchronized outputs. As a result, the approach requires expensive dedicated hardware.
Other current approaches provide a synchronized output by employing an approach that is sometimes referred to as time-based correction. This approach does not necessarily require the specialized hardware described above, however, time-based correction generally results in the loss of a frame-accurate playback of the signals because synchronization is achieved by adding repeat frames to an output signal that would otherwise advance out-of-sync and dropping other frames of the original data from the signal when the output has dropped behind the frame required for synchronization.
As used herein, a frame-accurate output refers to an output that, for a signal of original data that includes a plurality of frames, the output includes each of the frames in the same uninterrupted sequence as the frames appeared in the original data (e.g., the output does not include repeated frames, added frames, frame-deletions, and/or changes in the sequence of frames relative to the original data).
As one example of frame accuracy, the NTSC DVD format that is commonly used in the U.S. and Canada delivers 29.97 frames per second. Thus, a frame-accurate output corresponding to a NTSC formatted input includes each of the 29.97 frames in sequence that are provided in one second by the input without addition or deletion. Frame-accuracy does not require that the rate at which the original data is presented exactly match the rate of the input signal. In addition, frame-accuracy may apply to an output that corresponds to an input having any frame rate and in any format where the output may be in the same format or a different format than the original data.
Other approaches require that specialized hardware be installed with the computer to provide a frame accurate output in a plurality of output formats. That is, a commonly-available output for a PC cannot be used to supply a signal that integrates audio, video and graphics. In addition, currently available hardware is not hot-swappable, that is, the hardware cannot be connected to a computer when the computer is operational. Further, such specialized hardware generally lacks portability and is not platform compatible with a wide variety of commonly available platforms.